1. Field of the Invention
This invention generally relates to a linear motion guide unit suitable for use as a guide unit of various apparatuses such as high precision machining apparatuses and testing apparatuses, and, in particular, to such a linear motion rolling contact guide unit having a damper-inserted transverse adjustable mechanism for absorbing an error in alignment in the transverse direction.
2. Description of the Prior Art
A linear motion rolling contact guide unit is well known in the art and it generally includes a rail, a slider slidably mounted on the rail and a plurality of rolling members interposed between the rail and the slider so as to provide a relative rolling contact therebetween.
There are a number of different types of such a linear motion rolling contact guide unit. For example, in one type, a pair of inner guide grooves is formed on the opposite sides surfaces of the rail and the slider is generally U-shaped and formed with a pair of outer guide grooves each located opposite to an associated one of the inner guide grooves to thereby define a guide channel in which the rolling members are interposed between the rail and the slider. The slider is oriented upside down and slidably mounted on the rail in a straddling manner. With this structure, since there is basically provided no play between the rail and the slider in the lateral direction orthogonal to the longitudinal axis of the rail, the slider may move along the rail linearly at high accuracy.
The above-described type of linear motion rolling contact guide unit may not be suitable in some applications, in particular where it is desired that the slider be allowed to move in the lateral or transverse direction over some distance. One typical example of such a case is an application where two rails are provided in parallel and the sliders slidably mounted on these two rails are fixedly attached to a common table, as shown in FIG. 6.
In the structure shown in FIG. 6, a pair of elongated rails A and B are fixedly mounted on a base in parallel from each other. The rail A is generally rectangular in cross sectional shape and formed with a pair of inner guide grooves at its opposite side surfaces. A slider having a generally U-shaped cross section is slidably mounted on the rail A and formed with a pair of outer guide grooves each located in an opposed relationship with an associated one of the inner guide grooves to thereby define a guide channel. A plurality of rolling members are provided in the guide channel to provide a rolling contact between the rail A and its associated slider so that these rail A, slider and rolling members together define a linear motion rolling contact guide unit. Such a guide unit may be of the finite stroke type or the infinite stroke type. That is, the slider may be formed with a pair of endless circulating paths, each including a load path section, which corresponds to the above-mentioned guide channel, a return path section and a pair of curved connecting path sections each connecting the corresponding ends of the load and return path sections. With such an endless circulating path, theoretically an infinite relative motion may be provided between the rail and the slider. Without such an endless circulating path, the stroke of a relative motion between the rail and the slider is limited to a predetermined range.
A linear motion rolling contact table assembly shown in FIG. 5 also includes the other rail B which is arranged in parallel with the rail A. However, a tolerance is normally provided in the parallel arrangement between these two rails A and B from a practical viewpoint because there is a limit in the accuracy in arranging these two rails A and B in parallel. Because of such tolerance in the parallel arrangement between the two rails A and B, use can not be made of a linear motion rolling contact guide unit having the same structure as that having the rail A as described above. For this purpose, a linear motion rolling contact guide unit having the rail B has a structure different from that of the guide unit having the rail A.
That is, as shown in FIG. 6, the rail B has a generally T-shaped cross sectional shape because of the provision of a horizontally extending wing section C. The rail B is not provided with guide grooves as different from the rail A and instead it is formed with a flat guide surface E at its top surface. A slider D is slidably mounted on the rail B and it has a generally C-shaped cross sectional shape. The slider D is provided with four roller holders G and H, each including an endless circulating path provided with a plurality of rollers. Two of such roller holders G are in rolling contact with the top guide surface E of the rail B and the remaining two roller holders H are in rolling contact with bottom guide surfaces F of the wing sections C, respectively.
As described above, since the guide surfaces E and F are provided at the top and bottom surfaces of the wing sections C of the rail B, the slider D may shift in position in the lateral or transverse direction relative to the rail B as indicated by a double arrow I. As a result, if the range of such a relative motion in the lateral direction is selected to be slightly larger than the value of a tolerance set for the parallel arrangement between the two rails A and B, the common table fixedly attached to the two sliders associated with these rails A and B may move smoothly as guided by the rails A and B with a predetermined accuracy.
However, in the structure shown in FIG. 6, since a positive gap is provided between the rail B and the slider D, a problem arises when vibration is transmitted to the slider D externally, for example, from those elements mounted on the common table. Because of the presence of such a gap, a constant rattling motion may be produced in the slider D which in turn could cause wear, thereby deteriorating the performance. In addition, the presence of such a gap between the rail B and the slider D may cause an abrupt motion at the beginning of or ending of a relative motion between the rail B and the slider D. Thus, there is a tendency to deteriorate the accuracy in positioning of the slider D relative to the rail B.
With the structure shown in FIG. 6, in order to provide an accurate movement, the rolling contact between the rails A and B are their associated slider assemblies is preloaded or set with substantially zero tolerance. However, since there is a limit in arranging the rails A and B in parallel perfectly, there is normally an error in the degree of parallel arrangement. Thus, if the rails A and B extend over a relatively long distance, the true distance between the two rails A and B vary or fluctuate, so that the sliding resistance varies as the table assembly moves along the rails A and B. This is quite disadvantageous because of lack of smooth movement, possibility of excessive local wear and unreliability in operation. It is true that the problem could be relaxed if the rails A and B were aligned as accurately as possible. However, this would require an excessive care and skills in mounting the rails A and B on a common bed. For example, it would be almost impossible to arrange the rails A and B on the bed with an accuracy on the order of several tens of microns or less if the rails A and B are a few meters long.